I've read pretty much all the modern documents regarding pliosaurs science.

There is always a contradicting point between the various authors working on pliosaurs bones, the status of juveniles/adults regarding vertebral fusion.

The Aramberri pliosaur (Buchy 2003) is a particularly large pliosaur with some estimated pushing at around 15 m and is described with unfused vertebral centra and a state of co-ossification indicating a juvenile status.
However some other authors think giants pliosaurs were subject to paedomorphy. Still, even the most recent papers about large pliosaurs specimens are unclear about that and still seem to consider the non-fusion of the centra to be a reliable character of juvenile status in these animals.

The purpose of this question is that the possibility of a 15 m long, macrophagous, yet juvenile apex predator is appealing and in short I'd like to know if it is safe to consider the giant Mexican pliosaur as a juvenile, suggesting the existence of significantly larger adults ?

Furthermore Frey and Stinnesbeck (2014) report a tooth mark from another pliosaur that attacked the Aramberri specimen.
The tooth apparently punctured deeply the pterygoid, though no figure was available, and they claim to do this, the tooth crown must have been 30 cm long, which would be much larger than any known pliosaur tooth (the largest isolated teeth are 30 cm...complete).

Can this tooth mark (and the state of the Aramberri specimen) be considered reliable to valid the existence of super-giants (>20 m) pliosaurids in the Late Jurassic ?

sorry no-one seems to know the answer to your question.